The present invention relates to magnetic recording media, and more particularly relates to multilayer media having a columnar microstructure, which provides improved exchange decoupling and reduced noise.
Perpendicular magnetic recording systems have been developed for use in computer hard disc drives. A typical perpendicular recording head includes a trailing main pole, a leading return pole magnetically coupled to the main pole, and an electrically conductive magnetizing coil surrounding a yoke of the main pole. Conventional perpendicular recording media typically include a hard magnetic recording upperlayer and a soft magnetic underlayer, which provides a flux path from the trailing write pole to the leading return pole of the writer.
During recording operations, the perpendicular recording head is separated from the magnetic recording media by a distance known as the flying height. The magnetic recording media is moved past the recording head so that the recording head follows the tracks of the magnetic recording media, with the magnetic recording media first passing under the return pole and then passing under the main pole. Current is passed through the coil to create magnetic flux within the main pole. The magnetic flux passes from the main pole tip, through the hard magnetic recording track, into the soft underlayer, and across to the return pole.
One of the strongest candidates for perpendicular magnetic recording media includes a multilayer structure. Among the advantages of multilayers are easily adjusted anisotropy by varying the thickness of the layers in the bi-layer structure, and a remanence squareness equal to one, which ensures media with substantially no DC noise.
Multilayer-based perpendicular media is subject to a problem associated with conventional magnetic recording media. The magnetic grains must be exchange decoupled in order to improve signal-to-noise ratio (SNR). A typical multilayer recording structure comprises multiple repetitions of Co/Pt or Co/Pd bi-layers, which develop strong perpendicular anisotropy. The magnetic layers of the deposited films are granular, with each magnetic grain having a differing composition through its cross section. For these magnetic grains to be able to switch magnetization direction independently of each other, thus increasing SNR, they should be exchange decoupled.
A solution to this problem has been suggested recently by adding elements such as chromium to a magnetic layer such as Co in the bi-layer structure. Although this approach may help to exchange decouple the magnetic Co grains to some extent, since the non-magnetic Pt and Pd used in the spacer layers are highly polarizable elements, the exchange coupling will persist through the Pd or Pd spacer layers.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
The present invention effectively exchange decouples grains throughout a multilayer magnetic recording film. The multilayer film may be used as the hard magnetic recording film of a perpendicular magnetic recording medium. Although use of the present multilayer structures in perpendicular magnetic recording media is primarily described herein, it is to be understood that the present multilayer films may be used in other applications such as longitudinal magnetic recording media.
The multilayer film comprises alternating magnetic layers and nonmagnetic spacer layers. After deposition of the multilayers, the layers are exposed to an oxygen-containing atmosphere. The resultant multilayer film has a microstructure including granular columns. As used herein the term xe2x80x9cgranular columnsxe2x80x9d means crystalline grains which are generally aligned from layer-to-layer throughout substantially the entire thickness of the multilayer film. The granular columns extend in a direction substantially normal to the plane of the film. Within a particular column, the crystal structure of each magnetic layer and spacer layer may comprise a single grain, or may comprise multiple grains. The granular columns are separated by boundary layers which may be of lower density than the material of the granular columns.
During the oxygen treatment process, oxygen diffuses along the exterior of the columns and effectively exchange decouples the adjacent granular columns. The diffusion process may be accelerated through the use of elevated temperatures. In accordance with an embodiment of the present invention, additives such as B, Cr, SiO2 and the like may be added to the magnetic layers and the spacer layers. The additives may increase oxygen diffusion rates and increase oxidation in the boundary regions between adjacent granular columns. Such additives not only control exchange coupling between the granular columns, but also provide a mechanism to control the grain size.
An aspect of the present invention is to provide a magnetic recording media including a substrate and a hard magnetic recording film on the substrate comprising alternating layers of magnetic material and spacer material. The magnetic material and spacer material comprise a microstructure including granular columns separated by oxidized boundary layers.
Another aspect of the present invention is to provide an exchange decoupled magnetic recording film including alternating layers of magnetic material and spacer material. The magnetic material and spacer material comprise a microstructure including granular columns separated by oxidized boundary layers.
A further aspect of the present invention is to provide a method of making a magnetic recording film. The method includes the steps of depositing alternating layers of magnetic material and spacer material and treating the layers in an oxygen-containing atmosphere to produce oxidized boundary layers between granular columns of the layers.
These and other aspects of the present invention will be more apparent from the following description.